Equisetum telmateia (great horsetail or northern giant horsetail) is a species of Equisetum (horsetail) with an unusual distribution, with one subspecies native to Europe, western Asia and northwest Africa, and a second subspecies native to western North America. The North American subspecies is often simply but ambiguously called "giant horsetail", but that name may just as well refer to the Latin American Equisetum giganteum and Equisetum myriochaetum. It is found in damp shady places, spring fens and seepage lines, usually in open woodlands, commonly forming large clonal colonies.